clientserver.html

Beej的socket教材

    #include <sys/types.h>
    #include <netinet/in.h>
    #include <sys/socket.h>

    #define PORT 3490 // the port client will be connecting to 

    #define MAXDATASIZE 100 // max number of bytes we can get at once 

    int main(int argc, char *argv[])
    {
        int sockfd, numbytes;  
        char buf[MAXDATASIZE];
        struct hostent *he;
        struct sockaddr_in their_addr; // connector's address information 

        if (argc != 2) {
            fprintf(stderr,"usage: client hostname\n");
            exit(1);
        }

        if ((he=gethostbyname(argv[1])) == NULL) {  // get the host info 
            perror("gethostbyname");
            exit(1);
        }

        if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

        their_addr.sin_family = AF_INET;    // host byte order 
        their_addr.sin_port = htons(PORT);  // short, network byte order 
        their_addr.sin_addr = *((struct in_addr *)he->h_addr);
        memset(&(their_addr.sin_zero), '\0', 8);  // zero the rest of the struct 

        if (connect(sockfd, (struct sockaddr *)&their_addr,
                                              sizeof(struct sockaddr)) == -1) {
            perror("connect");
            exit(1);
        }

        if ((numbytes=recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1) {
            perror("recv");
            exit(1);
        }

        buf[numbytes] = '\0';

        printf("Received: %s",buf);

        close(sockfd);

        return 0;
    } 
</PRE
></TD
></TR
></TABLE
><P
>Notice that if you don't run the server before you run the client,
<TT
CLASS="function"
>connect()</TT
> returns "Connection refused".  Very
useful.</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="datagram"
>5.3. Datagram Sockets</A
></H2
><P
>I really don't have that much to talk about here, so I'll just
present a couple of sample programs: <TT
CLASS="filename"
>talker.c</TT
> and
<TT
CLASS="filename"
>listener.c</TT
>.</P
><P
><B
CLASS="command"
>listener</B
> sits on a machine waiting for an
incoming packet on port 4950.  <B
CLASS="command"
>talker</B
> sends a packet
to that port, on the specified machine, that contains whatever the user
enters on the command line.</P
><P
>Here is the <A
HREF="http://www.ecst.csuchico.edu/~beej/guide/net/examples/listener.c"
TARGET="_top"
>source for
<TT
CLASS="filename"
>listener.c</TT
></A
>:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;    /*
    ** listener.c -- a datagram sockets "server" demo
    */

    #include &#60;stdio.h&#62;
    #include &#60;stdlib.h&#62;
    #include &#60;unistd.h&#62;
    #include &#60;errno.h&#62;
    #include &#60;string.h&#62;
    #include &#60;sys/types.h&#62;
    #include &#60;sys/socket.h&#62;
    #include &#60;netinet/in.h&#62;
    #include &#60;arpa/inet.h&#62;

    #define MYPORT 4950    // the port users will be connecting to

    #define MAXBUFLEN 100

    int main(void)
    {
        int sockfd;
        struct sockaddr_in my_addr;    // my address information
        struct sockaddr_in their_addr; // connector's address information
        int addr_len, numbytes;
        char buf[MAXBUFLEN];

        if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

        my_addr.sin_family = AF_INET;         // host byte order
        my_addr.sin_port = htons(MYPORT);     // short, network byte order
        my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
        memset(&#38;(my_addr.sin_zero), '\0', 8); // zero the rest of the struct

        if (bind(sockfd, (struct sockaddr *)&#38;my_addr,
                                              sizeof(struct sockaddr)) == -1) {
            perror("bind");
            exit(1);
        }

        addr_len = sizeof(struct sockaddr);
        if ((numbytes=recvfrom(sockfd,buf, MAXBUFLEN-1, 0,
                           (struct sockaddr *)&#38;their_addr, &#38;addr_len)) == -1) {
            perror("recvfrom");
            exit(1);
        }

        printf("got packet from %s\n",inet_ntoa(their_addr.sin_addr));
        printf("packet is %d bytes long\n",numbytes);
        buf[numbytes] = '\0';
        printf("packet contains \"%s\"\n",buf);

        close(sockfd);

        return 0;
    } 
</PRE
></TD
></TR
></TABLE
><P
>Notice that in our call to <TT
CLASS="function"
>socket()</TT
> we're
finally using <TT
CLASS="constant"
>SOCK_DGRAM</TT
>.  Also, note that there's
no need to <TT
CLASS="function"
>listen()</TT
> or
<TT
CLASS="function"
>accept()</TT
>.  This is one of the perks of using
unconnected datagram sockets!</P
><P
>Next comes the <A
HREF="http://www.ecst.csuchico.edu/~beej/guide/net/examples/talker.c"
TARGET="_top"
>source for
<TT
CLASS="filename"
>talker.c</TT
></A
>:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;    /*
    ** talker.c -- a datagram "client" demo
    */

    #include &#60;stdio.h&#62;
    #include &#60;stdlib.h&#62;
    #include &#60;unistd.h&#62;
    #include &#60;errno.h&#62;
    #include &#60;string.h&#62;
    #include &#60;sys/types.h&#62;
    #include &#60;sys/socket.h&#62;
    #include &#60;netinet/in.h&#62;
    #include &#60;arpa/inet.h&#62;
    #include &#60;netdb.h&#62;

    #define MYPORT 4950    // the port users will be connecting to

    int main(int argc, char *argv[])
    {
        int sockfd;
        struct sockaddr_in their_addr; // connector's address information
        struct hostent *he;
        int numbytes;

        if (argc != 3) {
            fprintf(stderr,"usage: talker hostname message\n");
            exit(1);
        }

        if ((he=gethostbyname(argv[1])) == NULL) {  // get the host info
            perror("gethostbyname");
            exit(1);
        }

        if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
            perror("socket");
            exit(1);
        }

        their_addr.sin_family = AF_INET;     // host byte order
        their_addr.sin_port = htons(MYPORT); // short, network byte order
        their_addr.sin_addr = *((struct in_addr *)he-&#62;h_addr);
        memset(&#38;(their_addr.sin_zero), '\0', 8); // zero the rest of the struct

        if ((numbytes=sendto(sockfd, argv[2], strlen(argv[2]), 0,
             (struct sockaddr *)&#38;their_addr, sizeof(struct sockaddr))) == -1) {
            perror("sendto");
            exit(1);
        }

        printf("sent %d bytes to %s\n", numbytes,
                                               inet_ntoa(their_addr.sin_addr));

        close(sockfd);

        return 0;
    } 
</PRE
></TD
></TR
></TABLE
><P
>And that's all there is to it!  Run <B
CLASS="command"
>listener</B
> on
some machine, then run <B
CLASS="command"
>talker</B
> on another.  Watch them
communicate!  Fun G-rated excitement for the entire nuclear
family!</P
><P
>Except for one more tiny detail that I've mentioned many times in
the past: connected datagram sockets.  I need to talk about this here,
since we're in the datagram section of the document.  Let's say that
<B
CLASS="command"
>talker</B
> calls <TT
CLASS="function"
>connect()</TT
> and
specifies the <B
CLASS="command"
>listener</B
>'s address.  From that point
on, <B
CLASS="command"
>talker</B
> may only sent to and receive from the
address specified by <TT
CLASS="function"
>connect()</TT
>.  For this reason,
you don't have to use <TT
CLASS="function"
>sendto()</TT
> and
<TT
CLASS="function"
>recvfrom()</TT
>; you can simply use
<TT
CLASS="function"
>send()</TT
> and <TT
CLASS="function"
>recv()</TT
>.</P
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